Is there any way to combine PCs together?

I'm renting for a week+1 day and I have a PC for a free 1 day rental (no minimum days required) and also want to use a PC from the hertz site to get some $$ off my rental.

Normally, I'd just rent for 1 day using the free day coupon and the return it and rerent for a 1 week rental, but I'll be in another city with the car. Is there any way of getting around this?